Seal materials for potassium hydroxide-based electrolytic solution now in use for cells, particularly nickel-hydrogen cells, are mainly composed of hydrogenerated nitrile rubber. However, the hydrogenerated nitrile rubber has not satisfied yet the recent demand for longer life because of higher deterioration rate by the electrolytic solution. Furthermore, the seal materials for use at the electrode site of the nickel-hydrogen cell have a problem of energized deterioration.